The present invention relates to wireless communication systems, wherein wireless data transfers can be performed automatically when two modules come into proximity.
Systems which can provide short-range wireless data communication between a base station and a portable low-power module have recently been the subject of development efforts by a number of groups. Such systems can be extremely useful in many contexts, such as control of personnel access to secure facilities, medical monitoring of inpatients, automated livestock management, automated manufacturing generally, inventory control, theft control, and others described below.
However, such a system is subject to many constraints. First, the maximum power levels for RF (radio-frequency) emissions are stringently limited by law. Second, if the portability of the portable stations is to be maximized, the battery weight must be small, and this means that the power consumption of the portable module--in active or in standby mode--must be exceedingly low. Third, many possible applications are highly cost-sensitive. Moreover, in many such applications, the size and weight of the portable module are also extremely sensitive.
Such a system has the potential for great flexibility. However, the high-level organization of such a system must also be considered carefully. The communications protocols often assign the base station to be the master station. In such a typical configuration of this kind, each base station (unless passwording prevents this) can query, read, and write data to any portable module which may happen to be in range, without any independent action at the remote module.
A large system of this kind presents issues of access collision. If a large number of modules are within a base station's range, the base station may receive responses from many portable modules when it broadcasts a query signal. Each module has a "name" by which it can be addressed separately, but the use of module identifiers does not remove all problems: if a large number of modules may be present in the total system, the time for a base station to query the possible module identifiers may be large.
In the presently preferred embodiment, the identification field (which is 64 bits long in the presently preferred embodiment) can be parallel polled. By commanding all modules within range to respond, the base station can see the 64-bit identification fields combined in what is almost a "wired-OR" fashion. That is, if any one of the portable modules within range is pulsing (reporting a "1" bit) in a given time window, the base station will see a pulse; the base station will see the absence of a pulse only if all of the modules within range are reporting a "0" bit (not pulsing). This can be used, for example, to implement combinatorial logic functions on all (or some subfields of) the 64-bit identification field.
An example of the use of this capability is in secure facilities, for personnel access control. Suppose that every employee (or visitor or contractor) wears a badge, and that 10 bits of the identification field are used to indicate security clearance (at ten possible levels). One bit can be assigned to each level, so that each badge has only one "1" bit in this subfield. Then a base station can poll all badges in its area, and rapidly determine that there are no clearances below a certain level within range.